This is a multicenter, open-label, non-randomized, dual-arm pilot study to investigate the prevalence of the RT resistance mutations, K65R/x or L74V/x, in HIV-1 plasma from subjects experiencing confirmed first-time incomplete virologic suppression during treatment with an initial ARV regimen consisting of at least 12 weeks of TDF or ABC + FTC or 3TC + NNRTI or PI. Subjects will be followed until substantial loss of virologic or immunologic control requires a treatment switch. Confirmed first-time incomplete virologic suppression is defined as an initial plasma HIV-1 RNA response < 400 copies/mL, and subsequent virologic rebound > 400 copies/mL measured at two consecutive times.